The present invention relates to a method for producing cyclohexanol, and, more particularly, to an industrially useful improvement of the method for producing cyclohexanol by hydrating cyclohexene using a solid acid as a catalyst.
As methods for producing cycloalkanols by hydrating cycloolefins such as cyclohexene, methods which use solid acid catalysts such as strongly acidic ion exchange resins and zeolites as catalysts have been well known. A feature of these methods is that removal of the catalysts is easier as compared with removal of homogeneous system catalysts such as mineral acids, but these methods suffer from the problem of low yield. In order to improve the yield, it has been proposed to add various organic solvents or organic additives.
For example, JP-A-58-194828 proposes to add organic solvents such as alcohols of 1-10 carbon atoms, halogenated hydrocarbons, ethers, acetone and methyl ethyl ketone. JP-A-62-120333 and JP-A-62-126141 propose addition of phenols, JP-A-64-13044 proposes addition of fluoro-alcohols, JP-A-1-254634, JP-A-1-313447 and JP-A-4-247041 propose addition of aliphatic carboxylic acids, and JP-A-5-255162 proposes addition of benzoic acids. Moreover, JP-A-8-176041 proposes addition of benzoic acids having a substituent selected from the group consisting of alkoxy groups, aryloxy groups, alkylcarbonyl groups, arylcarbonyl groups, alkyloxycarbonyl groups, aryloxycarbonyl groups, aryl groups and arylalkyl groups. JP-A-9-263558 proposes addition of aromatic heterocyclic carboxylic acids. JP-A-7-247232 reports an effect exhibited by the coexistence with cycloalkanones, specifically, cyclohexanone. Furthermore, JP-A-9-249601 discloses a method in which a material having an action to enhance the distribution ratio of cycloalkenes into water is added alone or is allowed to coexist together with a material having an action to enhance the distribution ratio of cycloalkanols to organic layers, and it proposes addition of an alkylsulfonic acid or a heteropoly-acid in the former case and addition of an aromatic carboxylic acid, a phenol or a cyclic saturated carboxylic acid in the latter case. Moreover, in xe2x80x9cJournal of Japan Chemical Societyxe2x80x9d, 1989, (3), p.521-527, it is reported that the reaction rate and equilibrium conversion rate increase due to the presence of phenol, benzyl alcohol and methyl ethyl ketone.
However, these methods of adding various organic additives still have various problems in industrial working, and none of these methods can solve all of the problems. In many cases, there are problems that the yield is still insufficient even when the organic additives are used, and the use of solvents (organic additives) in large amounts is necessary for the improvement of the yield. Further problems are that the organic additives react with the starting material cyclohexene or the product cyclohexanol in the hydration reaction system, and the organic additives per se are not stable under the hydration reaction conditions, whereby by-products resulting from the organic additives are produced so as to cause loss of the organic additives and reduction in purity of the product cyclohexanol.
For example, use of the benzoic acid proposed in JP-A-5-255162, etc. has the problem that an esterification reaction takes place with the product cyclohexanol. Another problem is that purification of the reaction mixture by distillation is difficult to perform owing to the sublimation of benzoic acid.
In the case of using acetic acid proposed in JP-A-1-313447, since cyclohexyl acetate is produced in a large amount, a method for recovering each of cyclohexene, cyclohexanol and acetic acid is separately needed, which is disadvantageous for industrial working.
Although the phenols proposed in JP-A-62-120333, JP-A-62-126141, etc. are effective as solvents for improving the yield of cyclohexanol, since the cyclohexanol produced and the phenol form an azeotropic composition (maximum azeotropic point), there is a problem that distillation separation of cyclohexanol and phenol is impossible in industrial working, and, furthermore, there is a problem that since the solubility of phenol in water is high, namely, 8.5%, a loss of solvent increases in industrial working as mentioned hereinafter.
Benzyl alcohol disclosed in xe2x80x9cJournal of Japan Chemical Societyxe2x80x9d, 1989, (3), p.521-527 as a material having the effects of improving reaction rate and equilibrium conversion rate readily causes a hydration reaction under the hydration reaction conditions and is converted to dibenzyl ether, and, thus, the loss of solvent is great in industrial working. In addition, the above solvent effects cannot be obtained by dibenzyl ether and the effect of improving the conversion rate cannot be obtained.
Since cyclohexanone proposed in JP-A-7-247232 is somewhat lower in boiling point than the cyclohexanol to be produced, there will be a problem in distillation separation from cyclohexanol in industrial working. Furthermore, since cyclohexanone is also high in solubility in water, namely, 8.7%, there is a problem of an increase in loss of solvent in industrial practice.
On the other hand, new proposals have been made against these problems. For example, JP-A-9-286745 proposes to use a benzoic acid having a substituent on at least the 2-position as the organic additive to control esterification of the benzoic acid and the starting material cyclohexene. However, according to the examples in this patent publication, even when 2,6-dimethylbenzoic acid is used, complete inhibition of esterification thereof was not realized, and, further, the yield of cyclohexanol was only 14.7% by a batch reaction of 120xc2x0 C.xc3x971 hour using the additive in an amount of as large as 23 parts by weight. Thus, it cannot be said that a sufficient yield can be obtained.
JP-A-9-286746 proposes a method of using as an additive a cyclohexanecarboxylic acid having at least one substituent on the 1-, 2- or 6-position. According to the examples given therein, it is reported that the esterification can be inhibited by using 2-isopropylcyclohexanecarboxylic acid, but the yield of cyclohexanol is also only 13.6% by a batch reaction of 120xc2x0 C.xc3x971 hour using the additive in an amount of as large as 23 parts by weight. Thus, it cannot be said that a sufficient yield is obtained. Moreover, the organic additives used in these methods are extremely special ones.
On the other hand, for inhibiting deterioration of activity and for not deteriorating the performance of separation from the catalyst, JP-A-9-227429 and JP-A-9-227430 propose a method of feeding a solid organic additive in the molten state or as a solution to a reactor and a method of first contacting an aqueous slurry containing a solid acid catalyst with an organic additive in the presence of a cycloolefin. That is, in other words, it is suggested that the presence of the solid organic additive used in these methods has adverse effects of causing deterioration in catalyst activity with lapse of time and deterioration in separability of the catalyst in ordinary usage.
As mentioned above, the prior technologies as to the method of improving the yield of cyclohexanol by the addition of organic additives or solvents involve any one of the following problems in industrial practice.
1. The yield is still insufficient even when organic additive is used. Alternatively, a large amount of organic additive is necessary for improving the yield.
2. Impurities resulting from organic additive are produced in the hydration reaction system and the organic additive is lost with lapse of time, and, furthermore, the organic additive reacts with the starting material cyclohexene or the product cyclohexanol.
3. It is difficult to perform distillation separation between the organic additive per se or by-products resulting from the organic additive and the product cyclohexanol.
4. Deterioration of the activity of the hydration reaction catalyst is accelerated by the organic additive per se or by-products resulting from the organic additive.
5. The organic additive per se or by-products resulting from the organic additive adversely affect the separability between the catalyst and the reaction solution.
6. When the solvent (organic additive) is distributed into both phases of the cyclohexene phase and the aqueous phase and is high in solubility in the aqueous phase, problems arise in industrial practice. This is because in case there is a need to regenerate the catalyst in industrial practice, and when the reaction type is a stirring tank type which uses a catalyst slurry suspended in the aqueous phase, the solvent is also extracted out of the system together with the catalyst slurry in regeneration of the catalyst, and loss of the solvent added is great.
In the production of cyclohexanol by subjecting cyclohexene to hydration reaction in the presence of water using a solid acid as a catalyst, the present invention provides a solvent (an organic solvent) which can markedly improve the yield of cyclohexanol and simultaneously can solve all of the above-mentioned problems. Namely, according to the present invention, the yield of cyclohexanol can be markedly improved, no adverse effects are exerted on the selectivity of cyclohexanol, the change of catalyst activity with time or the separation of catalyst, and the product cyclohexanol can be easily recovered by distillation separation with only a small loss of solvent. Therefore, the object of the present invention is to provide a method for stably obtaining cyclohexanol of high purity in a very high yield.
As a result of intensive research conducted by the inventors in an attempt to solve the above problems, it has been found that in the production of cyclohexanol by subjecting cyclohexene to hydration reaction in the presence of water using a solid acid as a catalyst, the yield of cyclohexanol can be markedly improved, no adverse effects are exerted on the selectivity of cyclohexanol, the change of catalyst activity with time or the separation of catalyst, and the product cyclohexanol can be easily recovered by distillation separation with only a small loss of solvent, namely, cyclohexanol of high purity can be obtained stably and in a very high yield by using as a reaction solvent an organic solvent which is not higher than 5% by weight in solubility in water at 25xc2x0 C., has a boiling point which is at least 20xc2x0 C. higher than that of the cyclohexanol produced, is not more than 3% in conversion rate under the hydration reaction conditions, and is not less than 1.5 in solvent effect index which indicates the effect of making the distribution of cyclohexene into the aqueous phase predominate. Thus, the present invention has been accomplished.
That is, the present invention is a method for producing cyclohexanol by subjecting cyclohexene to a hydration reaction in the presence of water using a solid acid as a catalyst where an organic solvent which is not higher than 5% by weight in solubility in water at 25xc2x0 C., has a boiling point which is at least 20xc2x0 C. higher than that of the cyclohexanol produced, is not more than 3% in conversion rate under the hydration reaction conditions, and is not less than 1.5 in solvent effect index (which indicates the effect of making predominate the distribution of cyclohexene into the aqueous phase) is used as a reaction solvent. Preferably the solid acid is a zeolite, more preferably the zeolite is ZSM-5, and, furthermore, preferably the organic solvent used is isophorone or ethylene glycol monophenyl ether.
The present invention will be specifically explained below.
The solid acid used as a catalyst in the present invention is an acidic solid substance, and there may be used zeolites, acidic ion exchange resins, heterocyclic poly-acids, and acidic oxides substantially insoluble in water, such as zirconium dioxide, tin dioxide and titanium dioxide. Among them, zeolites are preferred. Zeolite is a general term for crystalline aliminosilicates. As zeolite-analogous substances, there are reported crystalline metallosilicates which are zeolites in which a part of Si or Al is substituted with B, Fe, Cr, Ti, Ge, Ga or the like, and these crystalline metallosilicates are also included in the zeolites of the present invention.
Examples of zeolites used in the present invention are A-type zeolites, X,Y-type faujasite, L-type zeolites, mordenite, offretite, erionite, ferrierite, zeolite xcex2, ZSM-4, ZSM-5, ZSM-8, ZSM-11, ZSM-12, ZSM-35, ZSM-48, etc. Preferred are zeolites having a pentasil structure, and especially preferred are ZSM-5 zeolites.
The zeolites used as catalysts in the present invention must be made into the acid type by ion exchange. The cation species introduced by ion exchange are not particularly limited as long as they can develop acidity, and mention may be made of, for example, protons, alkaline earth metals, metals of the titanium group, metals of the iron group, metals of the platinum group, rare earth metals, and the like. Among them, protons are preferred.
The organic solvents used as the reaction solvents in the method of the present invention have the following features. That is, the solubility in water at 25xc2x0 C. is not higher than 5% by weight, the boiling point is at least 20xc2x0 C. higher than that of the cyclohexanol produced, the conversion rate of the solvent under the hydration reaction conditions is not more than 3%, and the solvent effect index which indicates the effect of making the distribution of cyclohexene into the aqueous phase predominate is not less than 1.5.
The organic solvents used as the reaction solvents in the method of the present invention have a solubility in water at 25xc2x0 C. of lower than 5% because this is advantageous in industrial practice of the reaction. That is, when the reaction is industrially carried out by a stirring tank type method which uses a catalyst slurry suspended in an aqueous phase as disclosed in JP-B-2-31056 and JP-A-9-227430 together with a schematic view of a continuous flowing reaction apparatus, it is necessary to recover from the reactor a part of the catalyst slurry deteriorated in activity due to the use for a long period of time and to regenerate the catalyst. In this case, the solvent dissolved in the aqueous phase is also extracted to result in loss of the solvent dissolved in the aqueous phase. In case of an organic solvent high in solubility in water, it is necessary to recover the aqueous phase and the organic solvent dissolved in the aqueous phase from the catalyst slurry, for example, by filtration or the like, which is considerably disadvantageous.
Therefore, the solubility in water at 25xc2x0 C. of the organic solvent used as a reaction solvent in this reaction is preferably as low as possible, but the solubility correlates with the effect to make predominate the distribution of cyclohexene into the aqueous phase explained hereinafter, and, hence, the solubility in water at 25xc2x0 C. of the organic solvent is preferably not higher than 3% by weight, more preferably not higher than 1.5% by weight.
The organic solvent used as a reaction solvent in the method of the present invention is an organic solvent having a normal boiling point which is at least 20xc2x0 C. higher than that of cyclohexanol, namely, an organic solvent having a boiling point of not lower than 181xc2x0 C. Furthermore, it is preferred that distillation separation from the product cyclohexanol is possible. Here, xe2x80x9cdistillation separation is possiblexe2x80x9d means that the organic solvent used does not produce an azeotropic composition with cyclohexanol. These factors are advantageous because the distillation separation between the product and the reaction solvent can be simply performed by known methods. On the other hand, it is known that the phenol which is a reaction solvent showing a high solvent effect and disclosed in JP-A-62-120333 and JP-A-62-126141 produces an azeotropic composition with cyclohexanol and it is impossible to separate by distillation. Thus, this is industrially very disadvantageous.
The organic solvent used as a reaction solvent in the method of the present invention is preferably an organic solvent having a boiling point within the range of 181-230xc2x0 C. or 240xc2x0 C. or higher, and more preferably an organic solvent having a boiling point within the range of 185-220xc2x0 C., considering the separation from dicyclohexyl ether and cyclohexylcyclohexene which are high boiling point by-products in the cyclohexene hydration reaction.
The organic solvent used as a reaction solvent in the method of the present invention has a conversion rate of not more than 3% under the hydration reaction conditions of cyclohexene. The conversion rate of the organic solvent in the present invention is a conversion rate in the reaction of the organic solvent per se or the organic solvent with cyclohexene or cyclohexanol per 1 hour of batch reaction at the reaction temperature at which the hydration reaction of cyclohexene is carried out. In industrial working of the present invention, the solvent used for the reaction is separated from the product cyclohexanol and circulated for reuse. Therefore, taking into consideration the loss of the solvent and the product or the necessity for reuse of the solvent, preferably an organic solvent of not more than 1% in conversion rate under the hydration reaction conditions, more preferably an organic solvent that is substantially inert under the hydration reaction conditions (namely, does not react with cyclohexene and cyclohexanol) is used.
The organic solvent used as a reaction solvent in the method of the present invention exhibits an effect to make predominate the distribution of cyclohexene into an aqueous phase. The present reaction is carried out at a three-phase system of oil (cyclohexene)-water-catalyst. Since the solid acid catalyst such as zeolite is present in the aqueous phase and the reaction takes place on the catalyst, liquid-liquid distribution of cyclohexene greatly affects the reaction rate and the equilibrium conversion rate. As for the effect to make predominate the distribution of cyclohexene into the aqueous phase, xe2x80x9cJournal of Japan Chemical Societyxe2x80x9d, 1989, (3), p.521-527 mentions the results of measurement of the liquid-liquid distribution coefficient of cyclohexene in a solvent-free system and a phenol-containing system at 120xc2x0 C. According to the results, the cyclohexene distribution coefficient into both phases of oil and water (cyclohexene concentration in the oil phase (mol %)/cyclohexene concentration in the aqueous phase (mol %)) is 3818 in the solvent-free system while it is 680 in the phenol-containing system. That is, it can be seen that the distribution of cyclohexene into the aqueous phase becomes predominate due to the presence of phenol. In the specification of JP-A-9-249601, phenol is defined to be a substance enhancing the distribution rate of cyclohexanol into an organic phase, but according to the disclosure of xe2x80x9cJournal of Japan Chemical Societyxe2x80x9d, 1989, (3), p.521-527 and the results of a tracing test conducted by the inventors, it is considered that the effect of phenol to improve the yield is obtained by the effect of making predominate the distribution of cyclohexene into the aqueous phase.
The organic solvent used in the present invention has a solvent effect index (defined below) of not less than 1.5. The solvent effect index in the present invention is defined to be a ratio of a distribution coefficient of cyclohexene in the absence of solvent at 120xc2x0 C. and a distribution coefficient of cyclohexene in a solvent-containing system at 120xc2x0 C. (distribution coefficient of cyclohexene in the absence of solvent/distribution coefficient of cyclohexene in a solvent-containing system), and it indicates an effect to make predominate the distribution of cyclohexene into an aqueous solution due to the presence of the organic solvent.
Detailedly, the solvent effect index in the present invention is obtained in the following manner. Cyclohexene/cyclohexanol/organic solvent/water are charged at a weight ratio of 56.7/13.3/30/100, and the distribution coefficient of cyclohexene (molar fraction of cyclohexene in oil phase/molar fraction of cyclohexene in aqueous phase) is obtained from the liquid composition of both phases of the oil phase and the aqueous phase in an equilibrium state kept at 120xc2x0 C. The ratio of the resulting distribution coefficient of cyclohexene and the distribution coefficient of cyclohexene in a solvent-free system (measured at 120xc2x0 C. by charging cyclohexene/cyclohexanol/water at a weight ratio of 56.7/13.3/100), namely, the ratio of distribution coefficient in solvent-free system/distribution coefficient in solvent-containing system, is the solvent effect index in the present invention.
The organic solvent used in the present invention has a solvent effect index of not less than 1.5, preferably not less than 2. It is generally considered that the larger the solvent effect index, the greater the effect to make predominate the distribution of cyclohexene into the aqueous solution. However, the solvent effect index correlates with the solubility of the organic solvent in the aqueous phase, and the organic solvent is selected, considering the balance with the solubility in water as aforementioned.
Here, the distribution coefficient of cyclohexene is measured by the following method. That is, an oil and water at the above weight ratio are charged in a pressure container under a nitrogen pressure, and sufficiently stirred and mixed at a rising temperature of 120xc2x0 C., followed by reducing the stirring speed and leaving at rest for a time long enough to reach an equilibrium state. Thereafter, each of the oil phase and the aqueous phase is sampled in a solvent such as 1,4-dioxane, and the compositions of both the oil phase and the aqueous phase are obtained from analysis by gas chromatography and a Karl Fischer moisture meter. Thus, the distribution coefficient of cyclohexene is measured.
As examples of the organic solvents used in the present invention which have the above enumerated characteristics, mention may be made of phenethyl alcohol, ethylene glycol monophenyl ether (2-phenoxy ethanol), xcex1-isophorone (3,5,5-trimethyl-2-cyclohexen-1-one), xcex2-isophorone (3,5,5-trimethyl-3-cyclohexen-1-one), 2,4,4-trimethyl-2-cyclohexen-1-one, 3,3,5-trimethylcyclohexanone, 2,4,4-trimethylcyclohexanone, 2,6,6-trimethylcyclohexanone, 3,3,5,5-tetramethylcyclohexanone, etc. Preferred are ethylene glycol monophenyl ether and isophorones (which may be a mixture of xcex1-isophorone and xcex2-isophorone because they show similar solvent effects), and more preferred are isophorones. These organic solvents may be used each alone or in admixture of a plurality of them.
The characteristics of organic solvents used as reaction solvents in the present invention will be explained, taking as an example isophorone which is a preferable organic solvent.
The solubility in water at 25xc2x0 C. of isophorone which is a preferable organic solvent in the method of the present invention is 1.2 g/100 ml (see HAZARDOUS SUBSTANCES DATA BANK, ISOPHORONE, 920123). Isophorone produces a minimum azeotropic composition with water. Therefore, when the present reaction is industrially practiced by the stirring tank type method using a catalyst slurry suspended in an aqueous phase as shown above, use of isophorone is advantageous in that the amount of isophorone in the catalyst slurry extracted out of the system at the step of regeneration of catalyst is small, and, furthermore, it is also very advantageous in that isophorone in the catalyst slurry can be simply recovered by distillation utilizing the azeotropy with water and thus loss of the solvent can be considerably reduced.
As for the boiling point of isophorone, the boiling point of xcex1-isophorone is 215xc2x0 C. and that of xcex2-isophorone is 186xc2x0 C., and there is a difference of 25-50xc2x0 C. in the boiling point of isophorone and that of cyclohexanol, and, furthermore, since no azeotropic composition is produced, isophorone can be separated and recovered by the generally employed simple distillation separation methods.
Isophorone causes no hydration reaction under the reaction conditions of the present invention, and, further, has no reactivity with the starting material cyclohexene and the product cyclohexanol and is present very stably. Furthermore, due to its molecular structure, isophorone is hindered from diffusion into the pores of ZSM-5 zeolite suitably used in the present invention, and hence adverse effects on the catalyst activity can be avoided, selectivity for shape is also not affected, and, rather, the contribution of surface active points is inhibited resulting in an improvement in the selectivity of cyclohexanol. For this reason, isophorone is advantageous for industrial working.
The solvent effect index of isophorone obtained by carrying out the liquid-liquid equilibrium measurement shown above is 2.19, and it can be seen that isophorone is an organic solvent which makes predominate the distribution of cyclohexene into an aqueous phase.
As explained above, isophorone which is suitable as a reaction solvent in the method of the present invention develops the effect to make predominate the distribution of cyclohexene into the aqueous phase in spite of its low solubility in water, and, further, isophorone has the surprising effects that it can be easily separated from cyclohexanol by distillation and, furthermore, it has no adverse influence on the selectivity of cyclohexanol and change of catalyst activity with time. Thus, it can be said that isophorone is an excellent solvent which solves the problems in conventional methods for the production of cyclohexanol.
Isophorone is obtained by trimerization of acetone, and is used as industrial products comprising xcex1-isophorone containing a slight amount of xcex2-isophorone (isomer), mainly, as solvents for resins.
Isophorone is preferably of high purity, but industrial products may be used as they are. General purity of isophorone of industrial products is usually about 97-99.8% including xcex2-isophorone as an isomer.
The amount of water used in the method of the present invention is suitably 1-100 moles based on 1 mole of cyclohexene, and the amount of the catalyst used is suitably 0.01-100 in weight ratio based on cyclohexene. The amount of the organic solvent as a reaction solvent is 0.05-10, preferably 0.1-5, more preferably 0.25-1 in weight ratio based on cyclohexene.
The reaction type in the method of the present invention may be any of batch type, continuous type, reaction distillation type, and the like, and the continuous type includes the fixed-bed flowing reaction type and the stirring tank flowing reaction type.
The reaction temperature in the method of the present invention is 50-200xc2x0 C., preferably 80-160xc2x0 C. If the reaction temperature is lower than 50xc2x0 C., the reaction rate is slow, which is not practical, and if the reaction temperature exceeds 200xc2x0 C., equilibrium of the reaction is one-sided, which is disadvantageous.
The reaction pressure in the method of the resent invention is not particularly limited as long as a liquid phase is maintained at the reaction temperature, and is preferably 0.1-5 MPa. The reaction atmosphere is preferably an inert gas atmosphere such as nitrogen, helium, argon, carbon dioxide or the like, and preferably the oxygen content is low.
The present invention will be explained by the following examples. These examples should not be construed as limiting the invention in any manner, and changes and modifications may be made without departing from the spirit of the invention.